tests: Allow more tests to be skipped.

Specifically tests which involve btrfs, because btrfs is
currently broken upstream (RHBZ#863978).

tests/btrfs/test-btrfs-devices.sh

@@ -26,6 +26,12 @@ set -e
 
 guestfish=../../fish/guestfish
 
+# Allow the test to be skipped since btrfs is often broken.
+if [ -n "$SKIP_TEST_BTRFS_DEVICES_SH" ]; then
+    echo "$0: skipping test because environment variable is set."
+    exit 77
+fi
+
 # If btrfs is not available, bail.
 if ! $guestfish -a /dev/null run : available btrfs; then
     echo "$0: skipping test because btrfs is not available"

tests/btrfs/test-btrfs-subvolume-default.pl

@@ -24,6 +24,9 @@ use warnings;
 use Sys::Guestfs;
 use Sys::Guestfs::Lib qw(feature_available);
 
+# Allow the test to be skipped since btrfs is often broken.
+exit 77 if $ENV{SKIP_TEST_BTRFS_SUBVOLUME_DEFAULT_PL};
+
 my $testimg = "test1.img";
 
 unlink $testimg;

tests/charsets/test-charset-fidelity.c

@@ -77,12 +77,21 @@ static int feature_available (guestfs_h *g, const char *feature);
 int
 main (int argc, char *argv[])
 {
+  char *str;
   guestfs_h *g;
   char tmp[] = "/tmp/charsetXXXXXX";
   int fd;
   size_t i;
   struct filesystem *fs;
 
+  /* Allow this test to be skipped. */
+  str = getenv ("SKIP_TEST_CHARSET_FIDELITY");
+  if (str && STREQ (str, "1")) {
+    printf ("%s: test skipped because environment variable is set.\n",
+            argv[0]);
+    exit (77);
+  }
+
   g = guestfs_create ();
   if (g == NULL)
     error (EXIT_FAILURE, 0, "failed to create handle");