unsupported index on field names like $** and so on

[satebam]

Issue #, if available:

Description of changes:

MongoDB index on field $**:

> db.dummycol.createIndex({"$**": 1})
{
	"numIndexesBefore" : 1,
	"numIndexesAfter" : 2,
	"createdCollectionAutomatically" : true,
	"ok" : 1
}

DocumentDB index on field $**:

rs0 [direct: primary] test> db.dummycol.createIndex({"$**": 1})
MongoServerError: Index type not supported : $**

DocumentDB doesn't allow indexes on the field $, $, $*** and so on.

So, this PR is to capture this issue.

Sample output after change:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[tmcallaghan]

Requesting the following changes

• avoid the unnecessary complication of regex, a simple "in" should suffice
• rather than reporting "unsupported field names" call it out with something more precise like "wildcard indexes are not supported"

[satebam]

Requesting the following changes

• avoid the unnecessary complication of regex, a simple "in" should suffice
• rather than reporting "unsupported field names" call it out with something more precise like "wildcard indexes are not supported"

Made the fixes:

1. Removed the regex logic
2. Renamed unsupported field name s as UNSUPPORTED_WILDCARD_INDEXES

[tmcallaghan]

Closing, proper fix is in #175