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, the connection to the database is created using hostname and port from the configuration.

With Werk 15559 the invocation of tnsping was completely removed and 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. When the binary is available, the logic of mk_oracle is not modified. When the binary is not available, it is assumed that the tns-alias can be reached.

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