Merge branch 'stable-5.2' into stable-5.3

Merge branch 'stable-5.2' into stable-5.3

* stable-5.2:
  Fix NPE in RebaseTodoFile#parseComments
  Fix NPE in ObjectIdOwnerMap#get
  Fix NPE in CommitOnlyTest#getHead
  FileUtils#lastModifiedInstant should not log error if path doesn't exist
  Cache user global and system-wide git configurations
  Avoid setup and saving FileStoreAttributes compete for ~/.gitconfig lock
  Add missing dependencies for running FS_POSIXTest in Eclipse
  Fix javadoc for SystemReader#getInstance
  Improve retry handling when saving FileStoreAttributes fails
  Ensure FSTest uses MockSystemReader
  Make supportsAtomicCreateNewFile return true as default
  Update orbit to R20190602212107-2019-06 to enable backports from master
  Handle InvalidPathException in FS_POSIX#createNewFileAtomic
  Ensure root cause of lock creation failures is logged
  Implement toString in MockSystemReader and MockConfig
  LocalDiskRefTreeDatabaseTest shall use MockSystemReader
  Ensure LocalDiskRepositoryTestCase#setup fully uses MockSystemReader
  Ensure we use MockSystemReader in tests
  Override FileBasedConfig's save method in MockConfig
  Remove FileBasedConfig.load(boolean) introduced in d45219ba
  Disable debug log for FS in org.eclipse.jgit.test
  Bazel: enable logging for tests in org.eclipse.jgit.test
  LockFile: log exception if creation of lock file failed
  Stop using deprecated Constants.CHARACTER_ENCODING

Change-Id: If0c5010a2cf151ebebb2f2088fac3ee02c5007b9
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>