[maas] Fix maas dumpdata command not found Fixes: #423

The maas dumpdata command issued by the MAAS plugin causes a command
not found error. The command is now issued to maas-region-admin.

Also corrected capitalizations around the MAAS name.
Fixes: 423

Signed-off-by: Chris Johnston <chrisjohnston@ubuntu.com>
Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>