Add support for systemd-nspawn containers

This adds support for running OpenRC in a container created by
the systemd-nspawn utility.

This fixes #52.

X-Gentoo-Bug: 548058
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=548058

src/librc/librc.c

@@ -294,6 +294,8 @@ rc_sys_v1(void)
 		return RC_SYS_OPENVZ; /* old test */
 	else if (file_regex("/proc/1/environ", "container=lxc"))
 		return RC_SYS_LXC;
+	else if (file_regex("/proc/1/environ", "container=systemd-nspawn"))
+		return RC_SYS_SYSTEMD_NSPAWN;
 #endif
 
 	return NULL;

src/librc/rc.h.in

@@ -332,6 +332,7 @@ bool rc_service_daemons_crashed(const char *);
 #define RC_SYS_OPENVZ  "OPENVZ"
 #define RC_SYS_LXC     "LXC"
 #define RC_SYS_PREFIX  "PREFIX"
+#define RC_SYS_SYSTEMD_NSPAWN "SYSTEMD-NSPAWN"
 #define RC_SYS_UML     "UML"
 #define RC_SYS_VSERVER "VSERVER"
 #define RC_SYS_XEN0    "XEN0"