Don't assume redis_opts is enumerable

[ryansch]

When the redis configuration is just the url string and there's a connection error, exq raises an exception instead of displaying the error message.

[coveralls]

Coverage remained the same at 90.254% when pulling 78d07c6 on outstand:fix-redis-error-message into 250e7d6 on akira:master.

[coveralls]

Coverage remained the same at 90.254% when pulling 78d07c6 on outstand:fix-redis-error-message into 250e7d6 on akira:master.

[coveralls]

Coverage remained the same at 90.254% when pulling 7abbbc3 on outstand:fix-redis-error-message into 250e7d6 on akira:master.

[akira]

👍 thanks!