NXP-15891: Use a constant for UTC timezone in all the Drive implementations (to avoid thread locks on synchronized TimeZone.getTimeZone)

Conflicts:
	nuxeo-drive-core/src/main/java/org/nuxeo/drive/service/NuxeoDriveManager.java
	nuxeo-drive-core/src/main/java/org/nuxeo/drive/service/impl/NuxeoDriveManagerImpl.java
NXP-15891: Use Calendar.getInstance() directly instead of making a useless call to the service

Conflicts:
	nuxeo-drive-core/src/main/java/org/nuxeo/drive/service/NuxeoDriveManager.java
	nuxeo-drive-core/src/main/java/org/nuxeo/drive/service/impl/NuxeoDriveManagerImpl.java