Silent failure in Horizon when semantic checks prevent an action

[Maria Yousaf]

Brief Description
-----------------
Error messages as a result of semantic check validation are not being propagated to horizon

Severity
--------
Major

Steps to Reproduce
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- Lock a storage node in a storage group
- Attempt to lock the other storage node in the same group using Horizon
- The second lock silently fails without an error message being returned
- Meanwhile if the user checks the logs, the reason for the failure is given
- These error messages need to be propagated to horizon so the user has some feedback

Expected Behavior
------------------
Error messages and warnings displayed on the horizon console

Actual Behavior
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Silent failure when semantic checks prevent an action

Reproducibility
---------------
Reproducible

System Configuration
--------------------
Dedicated storage based system

Branch/Pull Time/Commit
-----------------------
designer build based on 2019-03-21 21:18:32 +0000, but the issue is believed to be a generic problem.

Last Pass
--------------
N/A

Timestamp/Logs
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2019-04-03 14:11:45.329 104779 WARNING wsme.api [-] Client-side error: Cannot lock a storage node when ceph pools are not empty and replication is lost. This may result in data loss.

[Ghada Khalil (gkhalil)]

Marking as release gating; issue with error propagation to horizon

[Maria Yousaf (myousaf)]

The fix for this issue was validated on build 20190419T013000Z.