Update Redis lock connection string parsing.

[hardlyknowem]

The previous code would fail to parse a password from a connection string if the password was empty. This uses the code used in, e.g., https://github.com/RichardKnop/machinery/blob/master/v1/brokers/redis/goredis.go#L43, as well as the backend.

[codecov]

Codecov Report

Merging #656 (2b9005f) into master (0d5824a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #656   +/-   ##
=======================================
  Coverage   37.41%   37.41%           
=======================================
  Files          36       36           
  Lines        3122     3122           
=======================================
  Hits         1168     1168           
  Misses       1806     1806           
  Partials      148      148           

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[RichardKnop]

👍