Rebalance slaves in tryserver.chromium for capacity.
Rebalance slaves in tryserver.chromium for capacity.

Proposed slaves rebalancing:

linux_chromium_chromeos_clang_rel: increase pool share to 20 slaves (from 15)
 * This builder is starved, but already shares a large linux pool.

win_chromium_x64_{rel,dbg}: add 20 slaves
 * Reclaim lost slave vm158-m4 (from win_tsan), see https://codereview.chromium.org/351863004
 * Move vmNNN-m4 from win8 pool to win7, NNN = range(318,337). Requires reimaging VMs to win7.
 * This pool is critically low on capacity.

mac_chromium_rel pool: add 15 slaves
 * Move 5 VMs [602, 604, 606, 608, 610] from mac_xcodebuild,mac_nacl_sdk pool
 * Merge 1 VM from mac_asan_64 to share the pool
 * Move 9 VMs from mac_x64_rel. Requires reimaging VMs 801-810 to 10.7 from 10.8.
 * This pool regularly has pending queues and is getting low on capacity.

mac_xcodebuild,mac_nacl_sdk pool: reduce pool to 1 slave (from 6)
 * donate slaves to mac_chromium_rel pool
 * It is very rarely used for manual try jobs.

mac_x64_rel: reduce pool to 1 slave (from 10)
 * donate slaves to mac_chromium_rel pool
 * It is very rarely used for manual try jobs.

win8_chromium_rel pool: reduce by 19 slaves
 * donate slaves to win_chromium_x64_rel pool.
 * This is a brand new pool, and at the moment is underutilized.

BUG=386438

Review URL: https://codereview.chromium.org/377373002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@283261 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build