version: Add metadata to MANIFEST errors

version::getValue didn't show any details about errors encountered
when parsing MANIFEST. Now it includes metadata about so that it's
more clear what went wrong in the MANIFEST file.

Tested: I modified the MANIFEST file in an image by removing the
purpose line, changed the version number to a new value, and
attempted to upload it onto a Rainier machine. The error message
matched the one I input, and the new metadata tags showed up as
"KEY" : "purpose=" and "ERROR" : "basic_ios::clear: iostream error"

Signed-off-by: Isaac Kurth <isaac.kurth@ibm.com>
Change-Id: I15e97752053c46f6b23cecfe762352a96a747134
1 file changed