Temp Feature: Halt-height

[youngjoon-lee]

The current panacead doesn't have the --halt-height flag which makes panacead stop when it reaches the halt-height.
But, we need it now to upgrade panacead with the new module did (That is, we cannot upgrade panacead without exporting the genesis).

By cosmos#4059, we'll get the --halt-height flag from the new cosmos-sdk v0.36.0+.
Until then, I'd suggest to cherry-pick the commit for --halt-height to the cosmos-sdk v0.35.6-internal. (I need to check if it's possible to cherry-pick it easily.)

Then, the upgrade process would be like:

[v1.2.5 -> v1.2.6]
1. sudo systemctl stop panacead
2. git checkout v1.2.6    (which has the --halt-height flag)
3. make build && make install && sudo cp $GOPATH/bin/panacea* /usr/local/bin/
4. panacead start --halt-height=XXXXX

[v1.2.6 -> v1.3.0]
1. Check if all panacead processes are stopped.
2. panacead export --for-zero-height --height=XXXXX > genesis_XXX.json
3. panacead unsafe-reset-all
4. git checkout v1.3.0
5. make build && make install && sudo cp $GOPATH/bin/panacea* /usr/local/bin/
6. sudo systemctl start panacead

Reference: https://github.com/cosmos/gaia/blob/master/docs/migration/cosmoshub-2.md