Fix heal_script for MySQL specifics

After running upgrade head->downgrade havana->upgrade head
on MySQL heal_script fails with several mistakes.

This change fix them. More details in related bug description.

Closes-bug: #1354218

Change-Id: I91cb21c4bc744f240bfb8bc6b2ed24b6e01f6095
Fix InvalidRequestError in auto_schedule_routers

This was discussed in review [1], and was deferred until the time was ripe
for the appropriate fix. As suggested and reported, auto_schedule_routers
is too affected by this error.

This patch takes care of the issue, in a similar way.

[1] - https://review.openstack.org/#/c/112740/

Related-bug: #1354072
Closes-bug: #1360104

Change-Id: Ie3cb0c31dfa571c694cd38e19f72ff8503815635
Check for IPv6 file before reading

Check to see if the IPv6 disabled flag file exists
before trying to read it. This file doesn't exist
on systems with the IPv6 module blacklisted.

Closes-Bug: #1361542
Change-Id: I4064b4189cc9d8f0f0e0e7025cf6f83d5b6ec276
Merge "Fix InvalidRequestError in auto_schedule_routers"
Merge "Check for IPv6 file before reading"
Merge "Fix heal_script for MySQL specifics"