RFR: 8220175: serviceability/dcmd/framework/VMVersionTest.java fails with a timeout

[Daniil Titov]

Please review the change that fixes an intermittent failure of serviceability/dcmd/framework/* tests on Linux platform.

The problem here is that get_namespace_pid() method, that is called by mmap_attach_shared () that in turn is called by PerfMemory::attach(),  
tries to read the namespace pid information from /proc/<pid>/status file. However, it doesn't check that the error indicator associated with 
stream is set that results in the endless  loop (lines 664-677) if the process terminates after /proc/<pid>/status was opened (line 659) 
and checked for null (line 661).

  658	  snprintf(fname, sizeof(fname), "/proc/%d/status", vmid);
   659	  FILE *fp = fopen(fname, "r");
   660	
   661	  if (fp) {
   662	    int pid, nspid;
   663	    int ret;
   664	    while (!feof(fp)) {
   665	      ret = fscanf(fp, "NSpid: %d %d", &pid, &nspid);
   666	      if (ret == 1) {
   667	        break;
   668	      }
   669	      if (ret == 2) {
   670	        retpid = nspid;
   671	        break;
   672	      }
   673	      for (;;) {
   674	        int ch = fgetc(fp);
   675	        if (ch == EOF || ch == (int)'\n') break;
   676	      }
   677	    }
   678	    fclose(fp);
   679	  }

The fix adds the check for the error indicator to ensure that the "while" loop terminates properly if the file no longer exists.

Issues [3] and [4] have the same cause and will be closed as duplicates of this issue.

Testing: Mach5 hotspot_serviceability tests succeeded, tier1,tier2, and tier3 tests are in progress.

[1] Webrev: http://cr.openjdk.java.net/~dtitov/8220175/webrev.01/
[2] Bug: https://bugs.openjdk.java.net/browse/JDK-8220175 
[3] https://bugs.openjdk.java.net/browse/JDK-8223600 
[4] https://bugs.openjdk.java.net/browse/JDK-8217351 

Thanks!
-Daniil