When trying to compare two values that are non-numeric using the driver
filter, the filter function will give an error. This is not desirable as
it might be interesting to support comparatives with non-numeric values
provided by the filter objects (share, host, etc). For example, the
following formula failed before the fix:
filter_function = '(share.project_id == "bb212f09317a4f4a8952ef3f729c2551")'
Copied from cinder 87a7e80a2c
Closes-Bug: #1975715
Change-Id: Icbfabb3bc0f608ebdd0784337db0921cc7763c53
