Replace code that assumes US/Pacific time zone

[andrewmwhite]

The LANDESK plugin (in the stethoscope/plugins/sources/landesk package) assumes a timezone of US/Pacific in a few places. These should be replaced with UTC and any comparisons elsewhere (like when last_sync is checked during filtering) should altered to make sure the conversion is done there instead of storing these as US/Pacific.

[suprithcs]

Hi Andrew, I've started to work on this. During filtering, we should convert to US/Pacific or local timezone?

[andrewmwhite]

Probably store as UTC and then check against local timezone when filtering.