Suggestion: Ability to run multiple alters on a single table

[Jericon]

The feature should be added to allow multiple --alter flags for a single table. This is particularly useful for alters around things such as partitioning, which cannot be done with other alters.

For example, I am currently doing multiple alters on a partitioned table. One to add a new index and another to remove partitioning. If I could specify multiple alters, I could do one to add the index and another to remove partitioning. The end result would be the same as if I ran two separate alters through gh-ost, but would make it so that only one would need to be done.

In the situation I am in now, the alters are estimated to take about 6 days, so being able to group them would be very beneficial.

[shlomi-noach]

duplicate: https://github.com/github/gh-ost/issues/512