travis: Fix execution of test from source tree setting skbuild platname

Since building the project specifying --plat-name or CMAKE_OSX_* variables
leads to different SKBUILD_DIR (e.g "_skbuild/macosx-10.6-x86_64-3.6" vs
"_skbuild/macosx-10.11-x86_64-3.6" , the code below attempt to guess the
most likely plat-name, extracting the plat-name from the first sub-directory
found under "_skbuild" directory.

Author: jcfr

Diff for: cmake/__init__.py

@@ -10,9 +10,21 @@
 
 CMAKE_DATA = os.path.join(os.path.dirname(__file__), 'data')
 
+
 # Support running tests from the source tree
 if not os.path.exists(CMAKE_DATA):
     from skbuild.constants import CMAKE_INSTALL_DIR as SKBUILD_CMAKE_INSTALL_DIR
+    from skbuild.constants import set_skbuild_plat_name
+
+    if platform.system().lower() == "darwin":
+        # Since building the project specifying --plat-name or CMAKE_OSX_* variables
+        # leads to different SKBUILD_DIR, the code below attempt to guess the most
+        # likely plat-name.
+        _skbuild_dirs = os.listdir(os.path.join(os.path.dirname(__file__), '..', '_skbuild'))
+        if _skbuild_dirs:
+            _likely_plat_name = '-'.join(_skbuild_dirs[0].split('-')[:3])
+            set_skbuild_plat_name(_likely_plat_name)
+
     _cmake_data = os.path.abspath(os.path.join(
         os.path.dirname(__file__), '..', SKBUILD_CMAKE_INSTALL_DIR(), 'cmake/data'))
     if os.path.exists(_cmake_data):