COMP: Fix sanity check associated with SlicerMacroConfigureGenericCxxModuleTests

The name of the variable and not its content was checked to be different
from an empty string.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21871 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Fix ExtensionsIndex experimental build error

Thanks to Chris Mullins for reporting the problem. Error is easily
reproducible when building an extensionsIndex with the option
-DSlicer_UPLOAD_EXTENSIONS:BOOL=ON. See below for detailed command
and associated error message.

Following commit r21860 ensuring target ExperimentalUpload, ExperimentalNightly,
... works as expected. The case when Slicer_UPLOAD_EXTENSIONS is ON and
the build is done manually instead of being driven by a dashboard hasn't been
tested :(

To fix the issue, we assume that by default a manual build of an
ExtensionsIndex corresponds to an Experimental build. The user can still
pass CTEST_MODEL at the command line if he wishes to change the value.

// -------------------
Error:

cmake -DSlicer_DIR:FILEPATH=/home/crmullin/Projects/Slicer4-SuperBuild-Debug/Slicer-build/ \
 -DSlicer_EXTENSION_DESCRIPTION_DIR:FILEPATH=/home/crmullin/ExtensionsIndexForTubetk/ \
 -DCMAKE_BUILD_TYPE:STRING=Release \
 -DSlicer_UPLOAD_EXTENSIONS:BOOL=ON \
 /home/crmullin/Slicer/Extensions/CMake/

[..]
Scanning dependencies of target JsonCpp
[  5%] Creating directories for 'JsonCpp'
[ 11%] Performing download step (git clone) for 'JsonCpp'
Cloning into 'JsonCpp'...
[...]
[ 16%] [ 22%] No patch step for 'JsonCpp'
Performing update step (git fetch) for 'JsonCpp'
HEAD is now at e2cfe02... Merge branch 'master' of github.com:TubeTK/jsoncpp-cmake
[ 27%] No configure step for 'JsonCpp'
[ 33%] No forcebuild step for 'JsonCpp'
[ 38%] Performing build step for 'JsonCpp'
* Extra verbosity turned on
Reading Script: /home/crmullin/Slicer/Extensions/CMake/SlicerBlockBuildPackageAndUploadExtension.cmake
SetCTestConfiguration:SourceDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp-build/Extensions-
SetCTestConfiguration:BuildDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp
Run dashboard with model TRACK
   Source directory: Extensions-
   Build directory: /home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp
CMake Error at /home/crmullin/Slicer/Extensions/CMake/SlicerBlockBuildPackageAndUploadExtension.cmake:90 (ctest_start):
  ctest_start given source path

    /home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp-build/Extensions-

  which is not an existing directory.  Set CTEST_CHECKOUT_COMMAND to a
  command line to create it.

SetCTestConfiguration:BuildDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp-build
SetCTestConfiguration:SourceDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp
SetCTestConfiguration:ConfigureCommand:"/home/crmullin/cmake-2.8.10.2/bin/cmake" "-DCMAKE_BUILD_TYPE:STRING=Release" "-GUnix Makefiles" "/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp"
SetCTestConfiguration:BuildDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp-build
SetCTestConfiguration:SourceDirectory:/home/crmullin/Projects/SlicerExtensionsIndex-tubetk/JsonCpp
Configure project
Current Tag empty, this may mean NightlyStartTime / CTEST_NIGHTLY_START_TIME was not set correctly. Or maybe you forgot to call ctest_start() before calling ctest_configure().
Cannot open configure file
Error in read script: /home/crmullin/Slicer/Extensions/CMake/SlicerBlockBuildPackageAndUploadExtension.cmake
make[2]: *** [JsonCpp-prefix/src/JsonCpp-stamp/JsonCpp-build] Error 255
make[1]: *** [CMakeFiles/JsonCpp.dir/all] Error 2
make: *** [all] Error 2

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21872 3bd1e089-480b-0410-8dfb-8563597acbee