[cmake] Read python name from PYTHON_BIN in cram module

.cmake/Modules/Cram.cmake

@@ -46,12 +46,10 @@ if (WIN32)
   endif ()
 endif ()
 
-execute_process (COMMAND python3 --version TIMEOUT 1 RESULT_VARIABLE PYTHON3_RES)
-
-if (NOT PYTHON3_RES STREQUAL "0")
+if (NOT ENV{PYTHON_BIN})
   set (PYTHON "python")
 else ()
-  set (PYTHON "python3")
+  set (PYTHON "$ENV{PYTHON_BIN}")
 endif ()
 
 execute_process (COMMAND ${PYTHON} -m cram -v ${CRAM_OPTS} "${CRAM_PATH}" TIMEOUT 60 RESULT_VARIABLE RES)

.travis.yml

@@ -103,8 +103,10 @@ before_install:
         if [ "$TRAVIS_OS_NAME" = "osx" ]; then
           brew install python3
           export PATH="$(python3 -m site --user-base)/bin:$PATH"
+          export PYTHON_BIN="python3"
         else
           curl -L https://bootstrap.pypa.io/get-pip.py | python3.5 - --user
+          export PYTHON_BIN="python3.5"
         fi
 
         pip3 install --user cram==0.6