Don't SIGABORT if device-mapper doesn't generate uevent for DeleteDevice

It looks like in some rare scenarios device-mapper won't create an
uevent while handling DM_DEV_REMOVE ioctl.

Since failure to generate uevent will result in ueventd not cleaning up
/dev paths in user space, it should be ok to just fail DeleteDevice call
without aborting the entire process.

Test: presubmit
Bug: 171266986
Change-Id: Iece28e6e02c35ac4bf33b9be74dfe1bbbb466bd4

Author: nioffe

fs_mgr/libdm/dm.cpp

@@ -111,8 +111,10 @@ bool DeviceMapper::DeleteDevice(const std::string& name,
 
     // Check to make sure appropriate uevent is generated so ueventd will
     // do the right thing and remove the corresponding device node and symlinks.
-    CHECK(io.flags & DM_UEVENT_GENERATED_FLAG)
-            << "Didn't generate uevent for [" << name << "] removal";
+    if ((io.flags & DM_UEVENT_GENERATED_FLAG) == 0) {
+        LOG(ERROR) << "Didn't generate uevent for [" << name << "] removal";
+        return false;
+    }
 
     if (timeout_ms <= std::chrono::milliseconds::zero()) {
         return true;