tests: workaround a bug in GNU grep

Workaround a bug introduced in GNU grep 2.27, for details see
https://lists.gnu.org/archive/html/bug-grep/2016-12/msg00011.html

* tests/init.sh (grep_pid_status): New function.
* tests/detach-running.test: Use it instead of grep to search
in /proc/$pid/status.
* tests/detach-sleeping.test: Likewise.
* tests/detach-stopped.test: Likewise.

tests/detach-running.test

@@ -79,8 +79,8 @@ if [ -f /proc/self/status ]; then
 		cleanup
 		dump_log_and_fail_with 'tracee died after detach'
 	}
-	grep '^State:.*R (running)' < /proc/$tracee_pid/status > /dev/null || {
-		grep '^State:' < /proc/$tracee_pid/status
+	grep_pid_status "$tracee_pid" '^State:.*R (running)' > /dev/null || {
+		grep_pid_status "$tracee_pid" '^State:'
 		cleanup
 		dump_log_and_fail_with 'tracee is not running after detach'
 	}

tests/detach-sleeping.test

@@ -80,8 +80,8 @@ if [ -f /proc/self/status ]; then
 		cleanup
 		dump_log_and_fail_with 'tracee died after detach'
 	}
-	grep '^State:.*S (sleeping)' < /proc/$tracee_pid/status > /dev/null || {
-		grep '^State:' < /proc/$tracee_pid/status
+	grep_pid_status "$tracee_pid" '^State:.*S (sleeping)' > /dev/null || {
+		grep_pid_status "$tracee_pid" '^State:'
 		cleanup
 		dump_log_and_fail_with 'tracee is not sleeping after detach'
 	}

tests/detach-stopped.test

@@ -95,8 +95,8 @@ if [ -f /proc/self/status ]; then
 		cleanup
 		dump_log_and_fail_with 'tracee died after detach'
 	}
-	grep '^State:.*T (stopped)' < /proc/$tracee_pid/status > /dev/null || {
-		grep '^State:' < /proc/$tracee_pid/status
+	grep_pid_status "$tracee_pid" '^State:.*T (stopped)' > /dev/null || {
+		grep_pid_status "$tracee_pid" '^State:'
 		cleanup
 		dump_log_and_fail_with 'tracee is not group-stopped after detach'
 	}

tests/init.sh

@@ -242,6 +242,14 @@ require_min_kernel_version_or_skip()
 		skip_ "the kernel release $uname_r is not $1 or newer"
 }
 
+# Usage: grep_pid_status $pid GREP-OPTIONS...
+grep_pid_status()
+{
+	local pid
+	pid=$1; shift
+	cat < "/proc/$pid/status" | grep "$@"
+}
+
 check_prog cat
 check_prog rm