CA-129192: Restore metadata for all SR

Revise restore-sr-metadata.py so that it could restore metadata for all SR
with command line:
   ./restore-sr-metadata.py -f <input file> -u all
or just omit the sr-uuid:
   ./restore-sr-metadata.py -f <input file>

xe-restore-metadata is modified accordingly.

Signed-off-by: Kaifeng Zhu <kaifeng.zhu@citrix.com>
CA-130011:Prevent xapi from filling it's buffer and running out of
memory while reading from an invalid device file
Signed-off-by: Akshay <akshay.ramani@citrix.com>
Merge pull request #1664 from kaifengz/CA-129192

CA-129192: Restore metadata for all SR
Merge pull request #1670 from akshayramani/XOP-529.a

CA-130011:Prevent xapi from filling it's buffer and running out of
CA-130748: Bumping down the xencenter max version to 2.1

Signed-off-by: Ravi Pandey <ravi.pandey@citrix.com>
Merge pull request #1809 from ravippandey/CA-130748

[SCTX-1849] CA-130748: Bumping down the xencenter max version to 2.1