dbt server fails to reload on HUP if docs block is missing enddocs tag

[drewbanin]

Describe the bug

When running the dbt server, invalid jinja code can cause the server to get stuck in a "compiling" state. This does not require partial parsing to be enabled.

Steps To Reproduce

1. Create a file, models/docs.md with the following contents:

{% docs abc%} hi {% enddocs %}

2. run dbt rpc
3. Modify models/docs.md to remove the enddocs tag
4. Send the dbt server process a SIGHUP signal
5. Observe that the status method on the server returns a compiling state

If you try to run a dbt compile (using dbt v0.15.1 or dev/0.15.2) with the same malformed docs block, you will see:

Running with dbt=0.15.2-a1
Encountered an error:
Traceback (most recent call last):
  File "/Users/drew/fishtown/dbt/core/dbt/main.py", line 80, in main
    results, succeeded = handle_and_check(args)
  File "/Users/drew/fishtown/dbt/core/dbt/main.py", line 158, in handle_and_check
    task, res = run_from_args(parsed)
  File "/Users/drew/fishtown/dbt/core/dbt/main.py", line 210, in run_from_args
    results = task.run()
  File "/Users/drew/fishtown/dbt/core/dbt/task/runnable.py", line 300, in run
    self._runtime_initialize()
  File "/Users/drew/fishtown/dbt/core/dbt/task/runnable.py", line 81, in _runtime_initialize
    super()._runtime_initialize()
  File "/Users/drew/fishtown/dbt/core/dbt/task/runnable.py", line 54, in _runtime_initialize
    self.load_manifest()
  File "/Users/drew/fishtown/dbt/core/dbt/task/runnable.py", line 46, in load_manifest
    self.manifest = get_full_manifest(self.config)
  File "/Users/drew/fishtown/dbt/core/dbt/perf_utils.py", line 23, in get_full_manifest
    return load_manifest(config, internal, set_header)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/manifest.py", line 441, in load_manifest
    return ManifestLoader.load_all(config, internal_manifest, macro_hook)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/manifest.py", line 329, in load_all
    loader.load(internal_manifest=internal_manifest)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/manifest.py", line 200, in load
    self.parse_project(project, macro_manifest, old_results)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/manifest.py", line 174, in parse_project
    self.parse_with_cache(path, parser, old_results)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/manifest.py", line 133, in parse_with_cache
    parser.parse_file(block)
  File "/Users/drew/fishtown/dbt/core/dbt/parser/docs.py", line 90, in parse_file
    for block in searcher:
  File "/Users/drew/fishtown/dbt/core/dbt/parser/search.py", line 125, in __iter__
    for block in self.extract_blocks(entry):
  File "/Users/drew/fishtown/dbt/core/dbt/parser/search.py", line 110, in extract_blocks
    collect_raw_data=False
  File "/Users/drew/fishtown/dbt/core/dbt/clients/jinja.py", line 399, in extract_toplevel_blocks
    collect_raw_data=collect_raw_data
  File "/Users/drew/fishtown/dbt/core/dbt/clients/_jinja_blocks.py", line 371, in lex_for_blocks
    collect_raw_data=collect_raw_data))
  File "/Users/drew/fishtown/dbt/core/dbt/clients/_jinja_blocks.py", line 362, in find_blocks
    ).format(self.current))
  File "/Users/drew/fishtown/dbt/core/dbt/exceptions.py", line 357, in raise_compiler_error
    raise CompilationException(msg, node)
dbt.exceptions.CompilationException: <exception str() failed>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/drew/fishtown/dbt/env/bin/dbt", line 7, in <module>
    exec(compile(f.read(), __file__, 'exec'))
  File "/Users/drew/fishtown/dbt/core/scripts/dbt", line 7, in <module>
    dbt.main.main(sys.argv[1:])
  File "/Users/drew/fishtown/dbt/core/dbt/main.py", line 96, in main
    logger.warning(str(e))
  File "/Users/drew/fishtown/dbt/core/dbt/exceptions.py", line 99, in __str__
    node_string = " in {}".format(self.node_to_string(self.node))
  File "/Users/drew/fishtown/dbt/core/dbt/exceptions.py", line 66, in node_to_string
    node.resource_type,
AttributeError: 'NotImplementedType' object has no attribute 'resource_type'

My guess is that this that the exception raised during exception handling is the culprit here, but I'm not certain of that.

Expected behavior

I would expect the server to be in an "error" state after HUPing the server with invalid dbt code.

The output of dbt --version:
Reproduced with v0.15.1 and dev/0.15.2

The operating system you're using: macOS