Improvements for testing with external data.

- flexible AddTest() parameter parsing
- added parameter for
  - executable arguments
  - referenced external data files
  - diff data files
- gives fatal errors when a requirement for a specific wrapper or tester is not met

see Applications/CLI/Tests.cmake b/Applications/CLI/Tests.cmake
Fix travis build temporarily, tester test depends on wrapper test.
Allow for test executable which are not targets of ogs, e.g. mpirun.
Added target sync-data on envinf1 only.

This copies all file from ${CMAKE_SOURCE_DIR}/../ogs6-data to
/data/ogs/ogs6-data and then triggers a build on Jenkins which
syncs /data/ogs6-data to opengeosys.org
Added mpirun-wrapper.
Make AddTest::PATH relative.

The new AddTest_SOURCE_PATH includes the
ExternalData_SOURCE_ROOT in AddTest.cmake.
Use AddTest_BINARY_PATH for simulation result file.

Used in the diff tester.
Remove debug message.
Merge pull request #7 from endJunction/test-improvements

Corrections for file paths in diff tester.
Correct comment.
Add numdiff tester.
Move up tester arguments for diff and numdiff.
Merge pull request #8 from endJunction/test-improvements

Test improvements
Install numdiff on travis.
Use the right diff tool.
Merge pull request #529 from bilke/test-improvements

Improvements for testing with external data