Tests table operations with lots of tablets

[keith-turner]

Some table operations read and write to the metadata table. In order to verify that these operations do not buffer too much in memory, testing with a large number of tablets would be good. Some of this testing is already done. Some table operations may need to be adapted to use the conditional tablet update changes in #3929 that avoid buffering conditional update status in memory.

• Delete table done in updates delete table to use conditional muations #3929
• Merge done in Updates merge code to support merging many tablets #3934
• Clone done in Updates merge code to support merging many tablets #3934
• Bulk import
• Compact done in adds support for compacting lots of tablets #3945
• Delete rows
• import/export
• offline/online

More test can be added to SplitMillionIT for the above cases.

[keith-turner]

Another useful test may be to create a table w/ lots of tablet, clone and truncate it. This simulates the situation where the user wants to create a copy of a range of a large table.