Summary:
During the gflags upgrade we can get current gflags state from nodes thus allowing us to skip
already processed nodes on retry.
This will also later allow us to implement rollback.
We check both server.conf and in-memory gflags (/varz endpoint)

Some details:
1) Tserver and master seems to write additional gflags (transaction_table_num_tablets, default_memory_limit_to_ram_ratio) to the end of the file, so we should ignore them if we see that desired state lacks these
2) Since /varz returns all the possible gflags, we compare only values, not the existance.

Test Plan:
sbt test
local provider test

Reviewers: nsingh, anijhawan, sanketh

Reviewed By: nsingh

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D46156