Validate nova server's metadata

This prevents "foo" getting passed into the metadata.
This can happen when using get_attr() to return a dynamic value.

Change-Id: I17eab659e65a51963e510add4d71fbc90a3a3a53
Closes-bug: #1338811
Adding missed whitespace between the words

Change-Id: I0103afc48ac795a49947643a1f79f41fcc914ee4
Merge "Adding missed whitespace between the words"
Merge "Validate nova server's metadata"