Automatic merge from submit-queue

Fix salt master check using hard coded string

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**What this PR does / why we need it**:
**Which issue this PR fixes** 
This is for vsphere only.

If var $INSTANCE_PREFIX is changed in cluster/vsphere/config-default.sh, then salt master check will fail due to the hard coded string "kubernetes-master".  The fix uses $MASTER_NAME instead.

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