Move file parser inquire calls to root PE

MOM_file_parser's open_param_file() contains explicit inquire() calls
when assessing the correctness of opening such a file.  As written,
these could be called by any rank, and are not thread safe.  In rare
cases (usually related to testing), this would cause a race condition
and raise an error.

Even ignoring the errors, it is probably better if only one rank makes
these calls, rather than all of them.

The following patch modifies the function so that only root PE invokes
inquire().

There is not much to celebrate about this patch; it does not try to
clean up the intrinsic weirdness of the IO handling.  But it does appear
to fix some of the most apparent problems.

src/framework/MOM_file_parser.F90

@@ -152,28 +152,34 @@ subroutine open_param_file(filename, CS, checkable, component, doc_file_dir)
   ! Check that this file has not already been opened
   if (CS%nfiles > 0) then
     reopened_file = .false.
-    inquire(file=trim(filename), number=iounit)
-    if (iounit /= -1) then
-      do i = 1, CS%nfiles
-        if (CS%iounit(i) == iounit) then
-          call assert(trim(CS%filename(1)) == trim(filename), &
-              "open_param_file: internal inconsistency! "//trim(filename)// &
-              " is registered as open but has the wrong unit number!")
-          call MOM_error(WARNING, &
-              "open_param_file: file "//trim(filename)// &
-              " has already been opened. This should NOT happen!"// &
-              " Did you specify the same file twice in a namelist?")
-          reopened_file = .true.
-        endif ! unit numbers
-      enddo ! i
+
+    if (is_root_pe()) then
+      inquire(file=trim(filename), number=iounit)
+      if (iounit /= -1) then
+        do i = 1, CS%nfiles
+          if (CS%iounit(i) == iounit) then
+            call assert(trim(CS%filename(1)) == trim(filename), &
+                "open_param_file: internal inconsistency! "//trim(filename)// &
+                " is registered as open but has the wrong unit number!")
+            call MOM_error(WARNING, &
+                "open_param_file: file "//trim(filename)// &
+                " has already been opened. This should NOT happen!"// &
+                " Did you specify the same file twice in a namelist?")
+            reopened_file = .true.
+          endif ! unit numbers
+        enddo ! i
+      endif
     endif
+
     if (any_across_PEs(reopened_file)) return
   endif
 
   ! Check that the file exists to readstdlog
-  inquire(file=trim(filename), exist=file_exists)
-  if (.not.file_exists) call MOM_error(FATAL, &
-      "open_param_file: Input file '"// trim(filename)//"' does not exist.")
+  if (is_root_pe()) then
+    inquire(file=trim(filename), exist=file_exists)
+    if (.not.file_exists) call MOM_error(FATAL, &
+        "open_param_file: Input file '"// trim(filename)//"' does not exist.")
+  endif
 
   Netcdf_file = .false.
   if (strlen > 3) then