Bug fix for distinting between string and map type tags in forms

[anuragaw]

Some APIs consume 'tags' param as string and some consume as maps.
Since each API can have at most one 'tags' param the extraction of
map based tags should only happen when strings based tags are not
extracted from the form serialization.

Description

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (improves an existing feature and functionality)
• Cleanup (Code refactoring and cleanup, that may add test cases)

Screenshots (if appropriate):

How Has This Been Tested?

Try tagging in 2 different places -

1. Snapshot , Snapshot policies
2. Disk offering creation

Both places should work. Without this patch only former would work.

[anuragaw]

ping for review - @rhtyd , @shwstppr , @nvazquez , @borisstoyanov , @PaulAngus

[yadvr]

lgtm, however, it's affects all users of the change and without testing it's hard to tell if it will cause any regressions

[anuragaw]

Tags extraction was a recent change I had worked on for supporting snapshot and snapshot policy tags. This was merged in the last few days . This PR change makes it more conservative and avoids overwriting of string based tags if any because a form should not contain multiple params with name 'tags'

[shwstppr]

LGTM. Tested manually

Before these changes tags in form data of create disk offering form is empty

After these changes, it shows the correct value

[borisstoyanov]

LGTM

[yadvr]

Merged based on reviews, manual test and screenshot.