Entity subscriptions are stored incorrectly

[echlebek]

Expected Behavior

Entity subscriptions are an array of subscriptions that are specified on the agent, plus an extra entity subscription added by the server.

i.e.

["eenie", "meenie", "miney", "moe", "entity:tiger"]

Current Behavior

["eenie,meenie,miney,moe", "entity:tiger"]

The array of subscriptions is always of length 2.

Steps to Reproduce (for bugs)

sensuctl entity list --format json | jq .[0].subscriptions

Context

Encountered while doing development work.

[echlebek]

Reproduced by @ccressent. @amdprophet observed that the problem only manifests when agents are launched with the --subscriptions flag. It seems that the subscriptions are not properly split in this case.