TOO RESTRICTIVE 

Analysis:
---------
Creating table using "CREATE TABLE [IF NOT EXISTS]" hangs
if table with same name already exists and if any other MDL
lock is taken on the lock object of the table.

While creating the table, we try to acquire "X" MDL lock on 
the lock object of the table. Lock will be acquired on table,
before even checking the existence of the table. Since "X"
is not compatible with any other MDL locks, if some other
lock is granted on the lock object of table then "X' lock
will not be granted and it will hang for lock timeout
period. 

Fix:
----
Acquiring "X" MDL lock before even checking for the existence
of table is resulting in the issue mentioned above. So, as 
a fix for this bug, modified a logic to acquire "S" lock and
check for the existence of the table. If the table does not
exists then upgrade lock to "X" and continue. If table exists
then,
      for "CREATE TABLE" - report an error.
      for "CREATE TABLE IF NOT EXISTS" - Push a warning.
and return.