Added a new function, osv::reboot() (declared in <osv/power.hh>)
for rebooting the VM.

Also added a Java interface - com.cloudius.util.Power.reboot().

NOTE: Power.java and/or jni/power.cc also need to be copied into
the mgmt submodule.

They are needed by the JVM when "-javaagent" command line option is
used. After this patch, the jamm memory meter javaagent can be enabled
for Cassandra.

Currently we statically link to libstdc++ and libgcc_s, and also dynamically
link to the same libraries (since the payload requires them).  This causes
some symbols to be available from both the static and dynamic version.

With the resolution order change introduced by 82513d41, we can
resolve the same symbol to different addresses at different times.  This
violates the One Definition Rule, and in fact breaks std::string's
destructor.

Fix by only linking in the libraries statically.  We use ld's --whole-archive
flag to bring in all symbols, including those that may be used by the payload
but not by the kernel.

Some symbols now become duplicates; we drop our version.

Lost during the romfs conversion.

We used to have libz in bootfs.manifest, and now that it was removed, it
needs to be put in usr.manifest... It is needed by Java to load the
compressed jar.