Add option to wait for machines to become available.
Add option to wait for machines to become available.

This option will allow hudson to start a process on an executor which runs
until some other process completes, without having to have general-purpose
process monitoring in place.

(really written by nshectman)


creative-quant/voltdb,migue/voltdb,flybird119/voltdb,creative-quant/voltdb,creative-quant/voltdb,deerwalk/voltdb,VoltDB/voltdb,VoltDB/voltdb,paulmartel/voltdb,simonzhangsm/voltdb,migue/voltdb,simonzhangsm/voltdb,paulmartel/voltdb,flybird119/voltdb,kobronson/cs-voltdb,paulmartel/voltdb,wolffcm/voltdb,migue/voltdb,zuowang/voltdb,kumarrus/voltdb,paulmartel/voltdb,flybird119/voltdb,migue/voltdb,migue/voltdb,simonzhangsm/voltdb,simonzhangsm/voltdb,creative-quant/voltdb,ingted/voltdb,migue/voltdb,kobronson/cs-voltdb,wolffcm/voltdb,zuowang/voltdb,ingted/voltdb,zuowang/voltdb,paulmartel/voltdb,creative-quant/voltdb,wolffcm/voltdb,kumarrus/voltdb,zuowang/voltdb,VoltDB/voltdb,flybird119/voltdb,deerwalk/voltdb,kobronson/cs-voltdb,creative-quant/voltdb,kobronson/cs-voltdb,ingted/voltdb,deerwalk/voltdb,kumarrus/voltdb,kumarrus/voltdb,kobronson/cs-voltdb,migue/voltdb,creative-quant/voltdb,VoltDB/voltdb,zuowang/voltdb,kobronson/cs-voltdb,simonzhangsm/voltdb,wolffcm/voltdb,wolffcm/voltdb,zuowang/voltdb,ingted/voltdb,flybird119/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,kumarrus/voltdb,kumarrus/voltdb,VoltDB/voltdb,kumarrus/voltdb,zuowang/voltdb,flybird119/voltdb,migue/voltdb,deerwalk/voltdb,wolffcm/voltdb,deerwalk/voltdb,creative-quant/voltdb,deerwalk/voltdb,wolffcm/voltdb,zuowang/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,simonzhangsm/voltdb,paulmartel/voltdb,ingted/voltdb,kumarrus/voltdb,ingted/voltdb,ingted/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,ingted/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,deerwalk/voltdb,wolffcm/voltdb,flybird119/voltdb,deerwalk/voltdb,flybird119/voltdb