[Fix #339] Update GitHub comment in deploy-pending-contracts scheduler thread

[vitvly]

Fixes #339

GitHub comments are now updated in a scheduler thread that attempted to redeploy pending contracts. Also, this PR removes unneeded code for failed contract redeployment and refactors contract deployment code to a separate fn.

[vitvly]

QA note: one way to test it would be post a bounty as usual, and then set transaction_hash field for the corresponding issue record to null. This will make that issue appear in the result set of pending-contracts query that is used by scheduler thread for redeployment.

Below the SQL query to set the transaction_hash for an issue with particular owner, repo, and issue_number:

update issues i
set transaction_hash=null, contract_address=null, comment_id=null
from repositories r
where r.repo=<repo-name>
and r.owner=<owner-name>
and i.repo_id=r.repo_id
and i.issue_number=<issue-number>;

[churik]

@siphiuel new comment from GH bot is not added, what I did wrong?

Steps:

• add new issue with bounty
• wait until contract will be deployed
• execute

update issues i
set transaction_hash=null, contract_address=null, comment_id=null
from repositories r
where r.repo=<repo-name>
and r.owner=<owner-name>
and i.repo_id=r.repo_id
and i.issue_number=<issue-number>;

• delete comment from GH bot
• wait ~ 15 mins

Expected result:

1. bounty is restored in open-bounty list
2. new comment from GH bot is added

Actual result:

1. bounty is restored in open-bounty list
2. no new comment is added
   Thus issue still haven't GH comment: Test4_to_delete_comment TestingEnvENV/TestEnvAtt5_1#33, but displayed in SOB in open-bounty list

NOTE: if I don't delete comment from GH bot, old comment is fully restored (with QR, contract address ect)

[churik]

Environments

• Ethereum wallet used: MetaMask
• Browser: Chrome
• Operating System: macOS High Sierra 10.13.3

Tested functionality

• Deploy and restore contract on ORG repo;
• Deploy and restore contract on personal repo;