examples/tls: support pre-shared key in examples
examples/tls: support pre-shared key in examples

This commit supports pre-shared key authentication in tls examples.

Change-Id: I16c0c4be015f048294257689bb3b83e3cfcf46ee
Signed-off-by: Junyeon LEE <ddc45265127aa1feb4b01be10ec1f0d25d062d3d@samsung.com>

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