fileVolume: Fix getChildren for NFS paths

Since NFS-based volume paths contain ':' characters, a simple split()
when parsing grep output will be problematic.  Better use rsplit(':', 1)
so we don't chop up the path unintentionally.

example:

/rhev/data-center/mnt/192.168.2.1:_home_storage_data/aa595433-e281-4886-ab75-6863552a19b9/images/04651881-b154-49f0-a6e0-ce15c66891aa/e42398c8-2073-4a62-b8c2-fd0aac1325bf.meta:PUUID=0b491657-066a-4d21-9464-b97b693325b2

should split to:
[0] /rhev/data-center/mnt/192.168.2.1:_home_storage_data/aa595433-e281-4886-ab75-6863552a19b9/images/04651881-b154-49f0-a6e0-ce15c66891aa/e42398c8-2073-4a62-b8c2-fd0aac1325bf.meta
[1] PUUID=0b491657-066a-4d21-9464-b97b693325b2

but right now we get:
[0] /rhev/data-center/mnt/192.168.2.1
[1] _home_storage_data/aa595433-e281-4886-ab75-6863552a19b9/images/04651881-b154-49f0-a6e0-ce15c66891aa/e42398c8-2073-4a62-b8c2-fd0aac1325bf.meta
[2] PUUID=0b491657-066a-4d21-9464-b97b693325b2

Change-Id: I43030a3f1ede6434675bde866007719416da0151
Signed-off-by: Adam Litke <alitke@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28871
Reviewed-by: Greg Padgett <gpadgett@redhat.com>
Tested-by: Greg Padgett <gpadgett@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>