Update vsphere image filename pattern

The vsphere image filename pattern has been updated so that semi-
colons are used to delimit image properties rather than colons,
which are not permitted in Windows filesystems. To support back-
wards compatibility, colons can still be used.

Change-Id: I29a3ac03dcae294326dc8813a66512a79f705f81
Closes-Bug: #1250319
Merge "Update vsphere image filename pattern"