[Packagemanager] Lock internal handle before set/unset event callback (#573)

[Packagemanager] Lock internal handle before set/unset event callback (#573)

* [Packagemanager] Fix typo

Change-Id: I4b1cfde45ccfe8d7d322e6835a8ac64a91c0c6b1
Signed-off-by: Sangyoon Jang <jeremy.jang@samsung.com>
* [Packagemanager] Lock internal handle before set/unset event callback

Since native API is not thread-safe, managed code should lock
SafePackageManager handle object before set/unset event callback.

Change-Id: I29ba6c9a24ec4c3f2aef8d017fd5bd9102f57cf8
Signed-off-by: Sangyoon Jang <jeremy.jang@samsung.com>