clean-up/rename storageMonitor -> spaceMon

[kirg]

• Fixes multiple minor issues in the 'storageMonitor'
  • potential race enabling/disabling write (create/stoppage of channel)
  • new go-routine created every cycle
  • ticker not stopped
  • avoid logging when not in warn/alert condition
  • remove two-way dependency between storehost and spaceMon
  • minor annoyance: rename 'storagemonitor" to "spaceMon" to reduce file completion collision with "storehost.go" on 'stor< tab >' .. :-)

[coveralls]

Coverage decreased (-0.2%) to 66.31% when pulling 87269bc88d8c50732b7d6ae07291864d4ce85948 on spaceMon into 27bdb2ba00f8f22cc97593526e2ec7920c316071 on master.

[coveralls]

Changes Unknown when pulling 10cf0d2668f15431eefbb9bbc978233645c85e86 on spaceMon into ** on master**.

[coveralls]

Changes Unknown when pulling 2954dd31196c7ff9873500701ce8aa22ecd8c2de on spaceMon into ** on master**.

[coveralls]

Changes Unknown when pulling 6b01dc9c7ce9abe95dec9606a1c2e4e827aec355 on spaceMon into ** on master**.

[coveralls]

Changes Unknown when pulling c22fe7edabcbbee7dc5496de758ae3e2d3f50753 on spaceMon into ** on master**.

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