Build adb if it's not available if users wants autoconnect.

Bug: 117584452
Test: m clean && m acloud && acloud create
Change-Id: I07d7927f69e3b18e51f9ffec6fa072c08a46a5e4
diff --git a/internal/lib/utils.py b/internal/lib/utils.py
index 4acacbc..fd12c31 100755
--- a/internal/lib/utils.py
+++ b/internal/lib/utils.py
@@ -47,13 +47,11 @@
 DEFAULT_RETRY_BACKOFF_FACTOR = 1
 DEFAULT_SLEEP_MULTIPLIER = 0
 
-SSH_BIN = "ssh"
 _SSH_TUNNEL_ARGS = ("-i %(rsa_key_file)s -o UserKnownHostsFile=/dev/null "
                     "-o StrictHostKeyChecking=no "
                     "-L %(vnc_port)d:127.0.0.1:%(target_vnc_port)d "
                     "-L %(adb_port)d:127.0.0.1:%(target_adb_port)d "
                     "-N -f -l %(ssh_user)s %(ip_addr)s")
-ADB_BIN = "adb"
 _ADB_CONNECT_ARGS = "connect 127.0.0.1:%(adb_port)d"
 # Store the ports that vnc/adb are forwarded to, both are integers.
 ForwardedPorts = collections.namedtuple("ForwardedPorts", [constants.VNC_PORT,
@@ -702,13 +700,13 @@
             "target_adb_port": target_adb_port,
             "ssh_user": ssh_user,
             "ip_addr": ip_addr}
-        _ExecuteCommand(SSH_BIN, ssh_tunnel_args.split())
+        _ExecuteCommand(constants.SSH_BIN, ssh_tunnel_args.split())
     except subprocess.CalledProcessError:
         PrintColorString("Failed to create ssh tunnels, retry with '#acloud "
                          "reconnect'.", TextColors.FAIL)
     try:
         adb_connect_args = _ADB_CONNECT_ARGS % {"adb_port": local_free_adb_port}
-        _ExecuteCommand(ADB_BIN, adb_connect_args.split())
+        _ExecuteCommand(constants.ADB_BIN, adb_connect_args.split())
     except subprocess.CalledProcessError:
         PrintColorString("Failed to adb connect, retry with "
                          "'#acloud reconnect'", TextColors.FAIL)