cmake: do not generate empty man pages

... when `csmock-common` is not installed on the system.  Also fix
the `rm -f ...` command, which was responsible to fail the build
of RPM packages in case the `help2man` command fails.

Fixes: commit da22c9d
PR: #208

Author: kdudka

.gitignore

@@ -1,2 +1,3 @@
 /csmock_build/
 /csmock-*.src.rpm
+__pycache__/

doc/CMakeLists.txt

@@ -28,11 +28,11 @@ add_custom_command(OUTPUT ${PROJECT_BINARY_DIR}/csmock/common
 # macro to generate a man page from the corresponding binary
 macro(create_manpage BINARY)
     add_custom_command(OUTPUT ${PROJECT_BINARY_DIR}/csmock/${BINARY}.1
-        COMMAND PYTHONPATH=${PROJECT_BINARY_DIR}/csmock ${HELP2MAN} --no-info
+        COMMAND PYTHONPATH=${PROJECT_BINARY_DIR} ${HELP2MAN} --no-info
         --section 1 --include ${CMAKE_CURRENT_SOURCE_DIR}/${BINARY}.h2m
           ${PROJECT_BINARY_DIR}/csmock/${BINARY}
         > ${PROJECT_BINARY_DIR}/csmock/${BINARY}.1
-        || rm -f ${PROJECT_BINARY_DIR}/${BINARY}.1
+        || rm -f ${PROJECT_BINARY_DIR}/csmock/${BINARY}.1
         COMMENT "Generating ${BINARY} man page"
         DEPENDS ${PROJECT_BINARY_DIR}/csmock/${BINARY}
                 ${PROJECT_BINARY_DIR}/csmock/common