message: Support cmake build on more linux slaves
  Default location for thirdparty_linux repo,
  as installed by jenkins job lynx-updateThirdPartyLinux,
  is ~/thirdparty-linux
  The env variable should be optional as a way to specify
  a different location rather than a mandatory step of slave
  configuration.
diff: @@ -59,8 +59,8 @@ if [ $(uname) = 'Darwin' ]; then
  #OSX be default is very verbose
  VERBOSE_CMAKE_ARG=
  else
  - #Currently require cmake installed on the slave
  - #todo - add it to thirdparty-linux
  + : ${THIRDPARTY_LINUX=~/thirdparty-linux}
  +
  CMAKE_EXE=${THIRDPARTY_LINUX:?this must be set}/tools/cmake-3.7.1-Linux-x86_64/bin/cmake
  GENERATOR="Unix Makefiles"
  