Fix dockerctl unlocking
Fix dockerctl unlocking

* replace $FDLOCK with correct file descriptor
* do an unlock before attaching to a container – it never exits unless
  killed by supervisord
* correctly redirect error message to stderr
* remove /var/lock/dockerctl

Closes-bug: 1513422
Change-Id: Idd70c381632e3dca7c24edab78a731dc03f363e1

ddepaoli3/fuel-library-dev,stackforge/fuel-library,stackforge/fuel-library,eayunstack/fuel-library,huntxu/fuel-library,stackforge/fuel-library,eayunstack/fuel-library,eayunstack/fuel-library,xarses/fuel-library,huntxu/fuel-library,eayunstack/fuel-library,ddepaoli3/fuel-library-dev,ddepaoli3/fuel-library-dev,xarses/fuel-library,stackforge/fuel-library,xarses/fuel-library,ddepaoli3/fuel-library-dev,huntxu/fuel-library,huntxu/fuel-library,ddepaoli3/fuel-library-dev,eayunstack/fuel-library,huntxu/fuel-library,xarses/fuel-library