Add v1 API x-image-meta- header whitelist

Add a whitelist of allowed 'x-image-meta-xxx' style
headers. Attempts to supply other, unexpected headers
will return 400.

This prevents cases such as 'x-image-meta-locations'
being processed, which were not being handled correctly.

Addresses bug 1205018.

Change-Id: I771bb6ae2a4f9cbd7726f952c7a71da99162b490
Merge "Add v1 API x-image-meta- header whitelist"