RDP cannot be used if home directory is not a writable directory

As noted in GUACAMOLE-927, the behavior of FreeRDP 2.0.0 differs from older versions of the library in that it depends on the existence of a writable home directory to initialize itself. It will refuse to attempt to connect if this is not the case. However, as recently noted on the user@ mailing list, users' home directories may be incorrectly set to files which are not actually directories or which are not writable, in which case the RDP connection will mysteriously fail.

As a valid, writable home directory is now a requirement for RDP to function, there should probably be additional sanity checks and warnings which ensure that a failure due to an invalid home directory can be easily diagnosed.