Refactor runMigrations and related provider methods

[svekko]

• Channel *Migration instead of interface on ret channel.
• Handle creating & closing the ret channel inside runMigrations.
• Handle provider error using a separate channel.
• Handle the case when runner exits (in case of an error) before the provider (read, readUp, readDown) has finished its job. Before the provider kept running in the background as there was nothing signalling it to exit.
• Create versionClean for internal use.

[coveralls]

Pull Request Test Coverage Report for Build 2001781023

• 99 of 144 (68.75%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 57.956%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
migrate.go	99	144	68.75%
<!--	Total:	99	144

Files with Coverage Reduction	New Missed Lines	%
migrate.go	4	73.57%
<!--	Total:	4

Totals
Change from base Build 1997075650:	0.1%
Covered Lines:	3737
Relevant Lines:	6448

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💛 - Coveralls