Werk #15289: mk_oracle: Revert werk 15559, use tnsping when available

Werk 15559 removed the invocation of tnsping.

tnsping was used to check if the tns-alias could be reached. If it could not be reached via tnsping, hostname and port is used to connect to the database.

With Werk 15559 the invocation of tnsping was completely removed. tns-alias was always used. This lead to problems with different configurations of mk_oracle.

This change introduces a check if the tnsping binary is available. If the binary is available, the logic of mk_oracle before Werk 15559 is restored. If the binary is not available, it is assumed that the tns-alias can be reached.

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