[XrdEcTests] Use different directory name for each test

This is necessary to avoid test failures when running tests in
parallel, as they'd be trying to overwrite each other's data in
that case, and also failing tests do not clean up after themselves,
so the following tests all fail if a given test fails.

tests/XrdEcTests/MicroTest.cc

@@ -280,13 +280,10 @@ void MicroTest::Init( bool usecrc32c )
   objcfg.reset( new ObjCfg( "test.txt", nbdata, nbparity, chsize, usecrc32c, true ) );
   rawdata.clear();
 
-  char cwdbuff[1024];
-  char *cwdptr = getcwd( cwdbuff, sizeof( cwdbuff ) );
-  CPPUNIT_ASSERT( cwdptr );
-  std::string cwd = cwdptr;
+  char tmpdir[32] = "/tmp/xrootd-xrdec-XXXXXX";
   // create the data directory
-  datadir = cwd + "/data";
-  CPPUNIT_ASSERT( mkdir( datadir.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH ) == 0 );
+  CPPUNIT_ASSERT( mkdtemp(tmpdir) );
+  datadir = tmpdir;
   // create a directory for each stripe
   size_t nbstrps = objcfg->nbdata + 2 * objcfg->nbparity;
   for( size_t i = 0; i < nbstrps; ++i )