init: Add support "&&" operator in property triggers

"&&" operator can now be used to test the validity
of two of more properties.

For example:

on property:test.a=1 && property:test.b=1
    setprop test.c 1

The above stub sets the test.c to 1 only when
both test.a=1 and test.b=1

(cherry-pick of 162f7d797c67019a7a3f08c3b0f0ffc91d548ddc.)

Change-Id: I72c19f7aa92231372a416193618ee6c7fd368141
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
diff --git a/init/readme.txt b/init/readme.txt
index 750d953..0b43fd5 100644
--- a/init/readme.txt
+++ b/init/readme.txt
@@ -123,6 +123,15 @@
    Triggers of this form occur when the property <name> is set
    to the specific value <value>.
 
+   One can also test Mutliple properties to execute a group
+   of commands. For example:
+
+   on property:test.a=1 && property:test.b=1
+       setprop test.c 1
+
+   The above stub sets test.c to 1 only when
+   both test.a=1 and test.b=1
+
 Commands
 --------