Fix devsds syntax error

[hirokikmr]

What this PR does / why we need it:
Fix devsds uninstall script syntax error.

+ osds::keystone::uninstall
+ '[' true '!=' 'false]'
/root/gopath/src/github.com/opensds/opensds/script/devsds/lib/keystone.sh: line 158: [: missing `]'

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

fixes #609

Special notes for your reviewer:

Release note:

[coveralls]

Coverage remained the same at 41.659% when pulling b03a7b8 on hirokikmr:development-bug-fix into 266321d on opensds:development.

[coveralls]

Coverage remained the same at 41.659% when pulling b03a7b8 on hirokikmr:development-bug-fix into 266321d on opensds:development.

[coveralls]

Coverage remained the same at 41.659% when pulling a248046 on hirokikmr:development-bug-fix into 266321d on opensds:development.

[xing-yang]

@hirokikmr Thanks for the fix!

[xing-yang]

lgtm