phosphor-user: add missing subprocess dependency

Change-Id: I47f464352b91c0c139227d2d06ca3698f7b17ca8
diff --git a/common/recipes-phosphor/users/obmc-phosphor-user.bb b/common/recipes-phosphor/users/obmc-phosphor-user.bb
index a307403..d30a394 100644
--- a/common/recipes-phosphor/users/obmc-phosphor-user.bb
+++ b/common/recipes-phosphor/users/obmc-phosphor-user.bb
@@ -10,7 +10,11 @@
 PROVIDES += "virtual/obmc-user-mgmt"
 RPROVIDES_${PN} += "virtual-obmc-user-mgmt"
 
-RDEPENDS_${PN} += "python-dbus python-pygobject python-pexpect"
+RDEPENDS_${PN} += " \
+        python-dbus \
+        python-pygobject \
+        python-subprocess \
+        python-pexpect"
 
 SRC_URI += "git://github.com/openbmc/phosphor-networkd"