[IOT-914] Change format of the device id as text string

[IOT-914] Change format of the device id as text string

DI field was being sent as a byte string over ther wire.

This patch update it to be sent as a string.

ocpayloadparse.c can handle both byte string and text string.
But ocpayloadconvert.c will be sending in text string.

Jira Issue: IOT-914
Signed-off-by: Habib Virji <habib.virji@samsung.com>
Change-Id: I049bf4cff5f2b390e589eb5cf55966e8034838b1
Reviewed-on: https://gerrit.iotivity.org/gerrit/5691
Reviewed-by: Dwarkaprasad Dayama <dwarka.dayama@samsung.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>