BUG: Manually specify Git executable in the Docker test build
BUG: Manually specify Git executable in the Docker test build

Addresses:

-- Setting default for EXTENSION_STATUS ........:
-- Found Git: /usr/bin/git
-- Found Subversion: /usr/bin/svn (found version "1.6.11")
CMake Error at
/usr/src/Slicer-build/VTKv7/CMake/NewCMake/FindPackageHandleStandardArgs.cmake:147
(message):
  Could NOT find Git (missing: GIT_EXECUTABLE)
  Call Stack (most recent call first):
  /usr/src/Slicer-build/VTKv7/CMake/NewCMake/FindPackageHandleStandardArgs.cmake:387 (_FPHSA_FAILURE_MESSAGE)
  /usr/src/Slicer/CMake/FindGit.cmake:175 (find_package_handle_standard_args)
  CMakeLists.txt:26 (find_package)
-- Configuring incomplete, errors occurred!

KitwareMedical/SlicerITKUltrasound,KitwareMedical/SlicerITKUltrasound