veyron/tools/mgmt: Support vrun inside of vbash.

Change-Id: I2bbfc439707f151d6538ba858dd36f2ba8683f5d
diff --git a/tools/mgmt/vbash b/tools/mgmt/vbash
index a2072c7..d1eb202 100755
--- a/tools/mgmt/vbash
+++ b/tools/mgmt/vbash
@@ -176,7 +176,7 @@
 export PS1="\${PS1}(\${GREENBOLD}\$(default_blessing)\[\033[0m\])$ "
 EOF
 
-VEYRON_CREDENTIALS="${CREDENTIALS_DIR}" exec "${BIN_INSTALL}/agentd" bash --rcfile "${INSTALL_DIR}/rcfile"
+VEYRON_CREDENTIALS="${CREDENTIALS_DIR}" exec "${BIN_INSTALL}/agentd" --additional_principals="${CREDENTIALS_DIR}" bash --rcfile "${INSTALL_DIR}/rcfile"
 }
 
 main "$@"