Move install to separate module

Build libinstall as a shared library. Also drop the dependency on the
global variables in common.h.

Test: unit tests pass, sideload an OTA
Change-Id: I30a20047768ce00689fc0e7851c1c5d712a365a0
diff --git a/recovery_main.cpp b/recovery_main.cpp
index 2f5a184..56ebe16 100644
--- a/recovery_main.cpp
+++ b/recovery_main.cpp
@@ -53,12 +53,12 @@
 #include "logging.h"
 #include "minadbd/minadbd.h"
 #include "otautil/paths.h"
+#include "otautil/roots.h"
 #include "otautil/sysutil.h"
 #include "recovery.h"
 #include "recovery_ui/device.h"
 #include "recovery_ui/stub_ui.h"
 #include "recovery_ui/ui.h"
-#include "roots.h"
 
 static constexpr const char* COMMAND_FILE = "/cache/recovery/command";
 static constexpr const char* LOCALE_FILE = "/cache/recovery/last_locale";