Disable HTTP keep-alive to avoid remote.http fd leak (CMC-1826)

[itzg]

Even when running the verify sub-command with the new repeat option I was able to observe an apparent leaking of FDs (example below). In http.Transport keep-alive is enabled by default and it appears the frequent re-connection is defeating/confusing Go's garbage collection of those connections.

COMMAND     PID     USER   FD      TYPE             DEVICE   SIZE/OFF       NODE NAME
___verify 13545 geof0549  cwd       DIR                1,4        224    4861757 /Users/geof0549/go/src/github.com/racker/rackspace-monitoring-poller/contrib/endpoint-agents/pzA/agentA/checks
___verify 13545 geof0549  txt       REG                1,4   15173348 8598597756 /private/var/folders/xf/96hzdx9n24s22r3_2wnw4_bxns4t3x/T/___verify_check__repeat_
___verify 13545 geof0549  txt       REG                1,4      32768 8598582046 /private/var/db/mds/messages/1804757117/se_SecurityMessages
___verify 13545 geof0549  txt       REG                1,4     837248 8598571787 /usr/lib/dyld
___verify 13545 geof0549  txt       REG                1,4 1156886528 8598581284 /private/var/db/dyld/dyld_shared_cache_x86_64h
___verify 13545 geof0549    0      PIPE 0x2307422e26013d1d      16384            ->0x2307422e2601539d
___verify 13545 geof0549    1      PIPE 0x2307422e26013ddd      16384            ->0x2307422e260158dd
___verify 13545 geof0549    2      PIPE 0x2307422e26012b1d      16384            ->0x2307422e26013a1d
___verify 13545 geof0549    3   NPOLICY
___verify 13545 geof0549    4u   KQUEUE                                          count=0, state=0xa
___verify 13545 geof0549    5u     unix 0x2307422e2918b935        0t0            ->0x2307422e2918cd85
___verify 13545 geof0549    6u     IPv4 0x2307422e270c4645        0t0        TCP office100-30.dfw1.rackspace.com:52556->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549    7r      CHR               14,1     0t4096        584 /dev/urandom
___verify 13545 geof0549    8u     IPv4 0x2307422e2850d0c5        0t0        TCP office100-30.dfw1.rackspace.com:52560->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549    9u     IPv4 0x2307422e26ff6645        0t0        TCP office100-30.dfw1.rackspace.com:52563->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   10u     IPv4 0x2307422e2708fce5        0t0        TCP office100-30.dfw1.rackspace.com:52565->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   11u     IPv4 0x2307422e2cc20ce5        0t0        TCP office100-30.dfw1.rackspace.com:52567->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   12u     IPv4 0x2307422e2cc21645        0t0        TCP office100-30.dfw1.rackspace.com:52569->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   13u     IPv4 0x2307422e2cc1fa25        0t0        TCP office100-30.dfw1.rackspace.com:52571->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   14u     IPv4 0x2307422e2cc1f0c5        0t0        TCP office100-30.dfw1.rackspace.com:52573->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   15u     IPv4 0x2307422e2719ba25        0t0        TCP office100-30.dfw1.rackspace.com:52575->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   16u     IPv4 0x2307422e18616a25        0t0        TCP office100-30.dfw1.rackspace.com:52577->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   17u     IPv4 0x2307422e16fdfce5        0t0        TCP office100-30.dfw1.rackspace.com:52582->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   18u     IPv4 0x2307422e18617385        0t0        TCP office100-30.dfw1.rackspace.com:52584->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   19u     IPv4 0x2307422e16fde0c5        0t0        TCP office100-30.dfw1.rackspace.com:52586->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   20u     IPv4 0x2307422e28a84ce5        0t0        TCP office100-30.dfw1.rackspace.com:52588->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   21u     IPv4 0x2307422e28a830c5        0t0        TCP office100-30.dfw1.rackspace.com:52590->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   22u     IPv4 0x2307422e28a83a25        0t0        TCP office100-30.dfw1.rackspace.com:52593->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   23u     IPv4 0x2307422e2cc20385        0t0        TCP office100-30.dfw1.rackspace.com:52595->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   24u     IPv4 0x2307422e275f4385        0t0        TCP office100-30.dfw1.rackspace.com:52597->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   25u     IPv4 0x2307422e275f5645        0t0        TCP office100-30.dfw1.rackspace.com:52599->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   26u     IPv4 0x2307422e275f30c5        0t0        TCP office100-30.dfw1.rackspace.com:52602->melange06.global.dfw.ohthree.com:https (ESTABLISHED)
___verify 13545 geof0549   27u     IPv4 0x2307422e184f0a25        0t0        TCP office100-30.dfw1.rackspace.com:52604->melange06.global.dfw.ohthree.com:https (ESTABLISHED)

[coveralls]

Coverage increased (+0.01%) to 61.149% when pulling 384e7e6 on fixes/http-check-fd-leak into 429086c on master.