Declare and initialize Attribute struct wherever possible

This change mostly gets rid of = { {0} } initialization.
Rename confusing variable 'classlist'

It actually holds a monitoring data to be written to the file, so name it so.
Group LoadSlowlyVaryingObservations together with other mon-related code
Fix cf-execd not reloading network and monitoring data

Environment reload was a huge bunch of copy-pasted-edited code,
so not all subsequent changes were applied to all agents at once.
Fix it by ensuring all agents unconditionally reload environment
in the same fashion.
Add missing time classes to cf-monitord
Remove long-outdated comment
No need to zero-initialize global variable
Split SetPolicyServer into two functions

Why $(sys.last_update_timestamp) was set in SetPolicyServer()?
Move POLICY_SERVER and sys.policy_hub initialization to single place

Previously it was scattered to several places, partially redundant.

Note that new clause in SetPolicyServer changes the behaviour, but
1) it is very rare case (policy_server.dat disappears during runtime)
2) this behaviour makes more sense: previously if policy_server.dat
disappeared, both POLICY_SERVER and sys.policy_hub retained old value
until process restart. After the change POLICY_SERVER and sys.policy_hub
pick up new value, even if it is "no file exists anymore"
Fix inclusion guards after rename
Remove unused variable
constify Policy
Merge pull request #1182 from dottedmag/refactoring/streamline-env-detection

Refactoring/streamline env detection