Use execvpe instead of execve in omnitrace-sample (#187)

* Use execvpe instead of execve in omnitrace-sample

- previous implementation preferred exe in PATH over exe in PWD
- 'p' variants of exec duplicate the actions of the shell in searching for an executable file if the specified filename does not contain a slash character

* OpenMPI oversubscribe arg in testing

VERSION

@@ -1 +1 @@
-1.7.2
+1.7.3