Storage object improvements.

* Convert all functions to variadic functions.
* Enforce read-only storage.
* Add storageLocalWrite() helper function. Add storageExists(), storagePathCreate(), storageRemove(), and storageStat().
* Add StorageFile object and storageOpenRead()/storageOpenWrite().

test/lib/pgBackRestTest/Common/DefineTest.pm

@@ -614,9 +614,19 @@ my $oTestDef =
                         'Storage/Helper' => TESTDEF_COVERAGE_PARTIAL,
                     },
                 },
+                {
+                    &TESTDEF_NAME => 'file',
+                    &TESTDEF_TOTAL => 1,
+                    &TESTDEF_C => true,
+
+                    &TESTDEF_COVERAGE =>
+                    {
+                        'storage/file' => TESTDEF_COVERAGE_FULL,
+                    },
+                },
                 {
                     &TESTDEF_NAME => 'storage',
-                    &TESTDEF_TOTAL => 4,
+                    &TESTDEF_TOTAL => 10,
                     &TESTDEF_C => true,
 
                     &TESTDEF_COVERAGE =>
@@ -626,7 +636,7 @@ my $oTestDef =
                 },
                 {
                     &TESTDEF_NAME => 'helper',
-                    &TESTDEF_TOTAL => 2,
+                    &TESTDEF_TOTAL => 3,
                     &TESTDEF_C => true,
 
                     &TESTDEF_COVERAGE =>