Server default timezone can be incorrect

Seen in server logs:

2017-03-09 09:44:38,771 | WARN | qtp943789296-23335 | (AbstractEventEndpoint:1623) - No 'capture.device.timezone' set on agent hoerilt1. The default server timezone Africa/Maseru will be used.

2017-03-09 09:48:58,191 | WARN | qtp943789296-23311 | (AbstractEventEndpoint:1623) - No 'capture.device.timezone' set on agent alex1c. The default server timezone UTC will be used.

This is logged in the getNewConflicts() method. At 9:44, the correct timezone is used, and at 9:48 the wrong timezone is used.

The default timezone is from:

TimeZone.getDefault().getID();

which is java.util.TimeZone.

We find elsewhere in the code, the default is being temporarily set to UTC here:

matterhorn-index-service/src/main/java/org/opencastproject/index/service/impl/IndexServiceImpl.java: TimeZone.setDefault(utc);

and here:

matterhorn-scheduler-impl/src/main/java/org/opencastproject/scheduler/impl/Util.java: TimeZone.setDefault(utc);

both in the calculatePeriods() method - not sure why that code is duplicated.

As the default is server-wide, changing the default timezone is not safe, because if this runs concurrently with another thread that relies on the default timezone, the second thread would get the wrong timezone.